The resignation of two oncologists at Royal Darwin Hospital has an advocacy group extremely concerned for cancer patients.

Louise Calvi, from NT Breast Cancer Voice, says, in a few weeks, one oncologist will remain at the Alan Walker Cancer Care Centre.

"It will mean there'll be a return to waiting lists," Ms Calvi said.

"We might now have to wait, for however long, before we're able to see a medical oncologist, in order to have that treatment started, and that could be a huge difference if it's a very aggressive cancer that requires treatment immediately."

The hospital has reportedly begun its recruitment process for the two positions.

Ms Calvi says flying up an oncologist from Royal Adelaide Hospital to help cope with demand isn't good enough.

"Bulldust is what I'd say to that," she said.

"Because patient care will be affected, because there isn't going to be that continuity of patient care, and there's not going to be even, probably, any handover from existing oncologists to any oncologists who are ... yet to be appointed."

"It's certainly not possible for one oncologist to do the work of three, and it's also not possible to ration the services for people that need the services of oncologists, which can't be delayed unnecessarily."